For example, a mesh filter is provided to a middle of an oil pipe in a fuel supply pipe, lubrication device, or the like that is connected to a fuel injection device of an automobile so as to filter out a foreign substance from a fluid such as a fuel or oil.
FIGS. 10A-10F show a conventional mesh filter 100. FIG. 10A is a front view of the conventional mesh filter 100, FIG. 10B is a side view of the conventional mesh filter 100, FIG. 10C is a cross-sectional view of the mesh filter 100 taken along line A8-A8 of FIG. 10A, and FIG. 10D is an enlarged view of a part B4 of FIG. 10A. Also, FIG. 10E is a cross-sectional view of a mold 101 for illustrating a first stage in a forming method of the conventional mesh filter 100, and FIG. 10F is a cross-sectional view of the mold 101 for illustrating a second stage in the forming method of the conventional mesh filter 100.
The conventional mesh filter 100 shown in FIGS. 10A to 10D includes: a mesh member 103 through which an oil can pass and on which a plurality of openings 102 which can filter out a foreign substance (such as metal powder and dust) of a predefined size are formed; a resin inner cylinder 104 installed along an inner circumferential edge of the mesh member 103; and a resin outer cylinder 105 installed along an outer circumferential edge of the mesh member 103. The mesh member 103 is in a hollow disk-like shape in planar view and formed by braiding nylon fibers 106 in a grid-like manner, and rectangular openings 102 are formed between the braided nylon fibers 106.
Such a conventional mesh filter 100 is insert-molded as shown in FIGS. 10E to 10F. First, a first mold 107 and a second mold 108 are opened and the mesh member 103 is placed on a pedestal 111 in a cavity 110 of the first mold 107 (see FIG. 10E). Then, the second mold 108 is pressed against the first mold 107 (the first mold 107 and the second mold 108 are clamped), the mesh member 103 is interposed between a pressing part 112 of the second mold 108 and the pedestal 111 of the first mold 107, and a cavity 110 is formed for molding an inner cylinder 104 and an outer cylinder 105 on a mold-matching surface 113 side of the first mold 107 and the second mold 108. Then, a melted resin is injected from a gate (not shown) into the cavity 110 to integrally form the resin inner cylinder 104 on an inner circumferential edge of the mesh member 103 and to integrally form the outer cylinder 105 on an outer circumferential edge of the mesh member 103 (see FIG. 10F). Such a technique of insert-molding a mesh filter 100 has been conventionally widely known (see Japanese Unexamined Utility Model Application Publication No. 5-44204 and Japanese Unexamined Patent Application Publication No. 2007-1232).
However, the conventional mesh filter 100 shown in FIGS. 10A to 10D is produced by insert molding, and an additional process for storing the mesh member 103 in a predetermined position in the cavity 110 is needed, thus requiring an increased number of production processes, compared to the case where a whole body is integrally formed by injection molding (see FIG. 10E). Also, in the conventional mesh filter 100 shown in FIGS. 10A to 10D, nylon fibers 106 braided in a grid-like manner are easily displaced and a shape and area (cross-sectional area of a flow path through which a fluid passes) of the openings 102 are easily varied, thus easily causing variation in filter performance (performance of removing a foreign substance of a predefined grain size or more).
Therefore, the applicant of the present application has developed a mesh filter 200 as shown in FIGS. 11A-11G in order to solve the above-described problems of the conventional insert-molded mesh filter 100 (see Japanese Unexamined Patent Application Publication No. 2015-61742). FIG. 11A is a front view of a mesh filter 200, FIG. 11B is a side view of the mesh filter 200, FIG. 11C is a rear view of the mesh filter 200, FIG. 11D is a cross-sectional view of the mesh filter 200 taken along a line A9-A9 of FIG. 11A, FIG. 11E is an enlarged view of a part B5 (a partially enlarged view of a filter part) of FIG. 11A, FIG. 11F is a cross-sectional view taken along a line A10-A10 of FIG. 11E, and FIG. 11G is a cross-sectional view taken along a line A11-A11 of FIG. 11E.
An entire body of the mesh filter 200 shown in FIGS. 11A-11G is integrally formed by injection molding, and a filter part 203 is integrally formed between an inner cylinder 201 and an outer cylinder 202. Also, the filter part 203 is configured to have openings 206 between adjacent horizontal bars 204, 204 and adjacent vertical bars 205, 205 that are perpendicular and adjacent to the horizontal bars 204, 204. Each of the openings 206 is formed in a square shape in planar view.
FIGS. 12A-12D show an injection-molding mold 207 for injection-molding such a conventional mesh filter 200. As shown in FIGS. 12A-12D, in the injection-molding mold 207, a cavity 212 is formed on a side of a mold-matching surface 211 of a first mold 208 and a second mold 210. The cavity 212 includes: a first cavity part 213 for forming the inner cylinder 201 of the mesh filter 200; a second cavity part 214 for forming the outer cylinder 202 of the mesh filter 200; and a third cavity part 215 for forming the filter part 203 of the mesh filter 200. Also, in the third cavity part 215, bar-like opening forming pins 216 of the same number as that of the openings 206 are formed for forming the openings 206. Further, each of the opening forming pin 216 is formed in a thin and long square-bar shape with a square-shaped tip surface 216a and a height L6 from a base end to the tip surface 216a is 0.3 mm same as the thickness L6 of the filter part 203.
In the mesh filter 200 that is injection-molded using the injection-molding mold 207 as such, a plurality of points on the inner cylinder 201 in a circumferential direction and a plurality of points on the outer cylinder 202 in a circumferential direction are pressed by a tip end surface of an ejector pin 217 when the mesh filter is released from the cavity 212 of the injection-molding mold 207. And, a releasing resistance between the opening 206 of the filter part 203 and the opening forming pin 216 of the injection-molding mold 207 tends to increase as the opening forming pin 216 forming the opening 206 of the filter part 203 is thinned. In this case, in the mesh filter 200, the filter part 203 deforms so as to be convex in a direction opposite to an extending direction of the ejector pin 217, and tends to cause a large stress on the thin and long opening forming pin 216 (see FIG. 12D). Therefore, the injection-molding mold 207 of the conventional mesh filter 200 requires highly-skilled labor in operational control during mold-releasing of the mesh filter 200.
Thus, the present invention provides an injection-molding method for a mesh filter, an injection-molding mold, and the mesh filter which can lessen the releasing resistance between the opening of the injection-molded mesh part and the opening forming pin of the injection-molding mold and reduce the stress caused on the opening forming pin.